To accommodate the IEEE 1588 standard for the Precision Time Protocol (PTP), it is convenient to monitor the Media Independent Interface (MII) for 10 and 100 BASE-T interfaces. The digital signals are interpreted to indicate a marker point, e.g. timestamp, for the departure and arrival of the Ethernet Frames, as they pass from the Media Access Layer (MAC) to the Physical Layer (PHY).
For 1000 BASE-T interfaces, the equivalent interface is the Gigabit Media Independent Interface (GMII). The trend in silicon fabrication is to integrate the MAC and PHY functions into the same device. This has created a difficulty for 1588 implementers who want to monitor these signals in a 1000 BASE-T environment since the GMII interface is not exposed.
Timing inaccuracies are introduced by the delays, delay asymmetries, and jitter from the following network related sources: PHYs, cables, and network devices, e.g. routers, switches, boundary clocks, and transparent clocks.